C.sub.8 alkylaromatic hydrocarbons are generally considered to be valuable products, with the demand for para-xylene being high and the demand for meta-xylene steadily increasing. In typical C.sub.8 alkylaromatic hydrocarbon formation processes, the reaction product contains a mixture of ethylbenzene, ortho-xylene, meta-xylene, and para-xylene. Therefore, the desired C.sub.8 alkylaromatic hydrocarbon isomer must be separated from the mixture. Historically, industry has sought ways to separate para-xylene, the most desired compound, from the mixture, and numerous patents exist to that end. For example, zeolites X and Y have been used to selectively adsorb para-xylene; see U.S. Pat. No. 3,903,187, U.S. Pat. No. 4,313,015, U.S. Pat. No. 5,171,922, U.S. Pat. No. 5,495,061 and U.S. Pat. No. 5,177,295. Similarly, U.S. Pat. No. 4,899,017 discloses contacting the C.sub.8 alkylaromatic hydrocarbon mixture with a zeolitic adsorbent selective for para-xylene and then contacting the adsorbent with a nonaqueous desorbent to recover the para-xylene from the adsorbent. The stated zeolitic adsorbents selective for para-xylene in U.S. Pat. No. 4,899,017 are ZSM-5, ZSM-11 and zeolite Beta. U.S. Pat. No. 4,940,830 discloses a rejective separation of para-xylene from other xylene isomers and ethylbenzene using sodium Y zeolite or a sodium Y zeolite ion exchanged with an element from Groups IB or VII of the Periodic Table.
With growing interest in meta-xylene, patents directed to the separation of meta-xylene are becoming more numerous. For example, U.S. Pat. No. 5,382,747 discloses adsorbing meta-xylene using a sodium or sodium and lithium exchanged Y zeolite to separate meta-xylene from a mixture of C.sub.8 aromatic hydrocarbons including other xylenes in the liquid phase. U.S. Pat. No. 4,368,347 discloses a rejective separation of meta-xylene using zeolite Y preliminarily exchanged with potassium.
Applicants have discovered that a particular adsorbent, zeolite Beta, is effective in separating meta-xylene from a mixture of C.sub.8 alkylaromatic hydrocarbons. Zeolite Beta has been used to separate isomers of C.sub.9 aromatic hydrocarbons (U.S. Pat. No. 4,554,398) and C.sub.10 aromatic hydrocarbons (U.S. Pat. No. 4,743,708). Zeolite Beta has also been used to selectively adsorb ethylbenzene from a stream containing ethylbenzene and one or more isomeric xylenes, (U.S. Pat. No. 4,584,424) and to selectively adsorb para-xylene from a stream containing para-xylene and another C.sub.8 aromatic hydrocarbon (U.S. Pat. No. 4,899,617). Applicants have discovered that zeolite Beta is uniquely suited to the separation of meta-xylene from other xylene isomers since zeolite Beta preferentially rejects meta-xylene as compared to the other xylene isomers. Therefore, the meta-xylene of a mixture of xylene isomers that is in contact with zeolite Beta will be carried with the fluid flow, while the other isomers are retained by the zeolite Beta thereby allowing for the recovery of separated meta-xylene.